New Study Points to Correlation Between Legionella and Cooling Towers

LegionellaA peer-reviewed article on Legionella pneumophila growth in cooling towers has been published in the UK-based Journal of Water & Health, an official journal of the World Health Organization and the International Water Association. Authored by Christopher Radziminski, M.A.Sc., CWP, P.Eng, City of Vancouver Building Policy Engineer, and Phillip White, Manager, Plumbing and Mechanical Inspections, the article presents Legionella pneumophila results (from a culture-based method) for 557 cooling towers across Vancouver for 2021. Results of 10 CFU/mL or greater (defined as exceedances) were reported for 30 cooling towers (5.4 percent), including six with more than 1,000 CFU/mL, and L. pneumophila serogroup 1 (sg1) was identified in 17 of these cooling towers (out of 28 with serogroup-level analysis).

The data indicate highly localized Legionella issues, with exceedances concentrated within 16 facilities, including two hospitals. In the three months preceding each cooling tower exceedance, the nearest municipal water-sampling station had a free chlorine residual of at least 0.46 mg/L and a temperature of <20°C. There was not a statistically significant correlation between the L. pneumophila concentration of a cooling tower in exceedance and the municipal water’s free chlorine residual, temperature, pH, turbidity, or conductivity. There was a statistically significant negative correlation between the concentrations of L. pneumophila sg1 and other L. pneumophila serogroups in cooling towers. This unique dataset underscores the pivotal role of building owners and managers in preventing the growth of Legionella bacteria and the value of regulations to verify operations and maintenance practices.

You can read the results and analysis in the Journal of Water & Health.

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